Friction material

ABSTRACT

AN IMPROVED FRICTION MATERIAL FOR FRICTION-ENGAGING MECHANISMS, SUCH AS AUTOMOTIVE BRAKES AND CLUCHES, COMPRISING ABOUT 30 TO 80% OF IRON OXIDE POWDER WHOSE MAIN INGREDIENT IS FERROSOFERRIC OXIDE, SUCH AS IRON SAND, ABOUT 15 TO 65% OF ORGANIC BINDER, AND THE BALANCE OF FILLERS AND ADDITIVES, WHEREBY TO IMPROVE WEAR, REDUCE DEFACEMENT AND PROVIDE A SUBSTANTIALLY CONSTANT COEFFICIENT OF FRICTION.

May 1W2 KIYOSHA NINOMIYA ETAL 3, 6,49

FRICTIQN MATERIAL Filed Sept. 16, 1970 2 Shee'hS Sheet 2 FIG. 4 Fl IN VEN TORS. ,v/ YO s/w Nl/VOM Y4, H/DEAK/ 04/424,

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United States Patent US. Cl. 26038 4 Claims ABSTRACT OF THE DISCLOSURE-An improved friction material for friction-engaging mechanisms, such asautomotive brakes and clutches, comprising about 30 to 80% of iron oxidepowder whose main ingredient is ferrosoferric oxide, such as iron sand,about 15 to 65% of organic binder, and the balance of fillers andadditives, whereby to improve wear, reduce defacement and provide asubstantially constant coefficient of friction.

This application is a continuation-in-part of applicants previouslyfiled application Ser. No. 723,350, filed Apr. 19, 1968, and entitledFriction Material, now abandoned.

This invention relates to an improved friction material forfriction-engaging mechanisms, and more particularly to a molded frictionlining material for automotive brakes and clutches, and the like.

The optimum properties of a good friction material for automotive brakelinings and the like are: an adequate coefiicient of friction for theexpected usage, the ability to retain a substantially constantcoefiicient of friction under varying conditions such as rubbing surfacetemperature, rubbing surface pressure, and rubbing surface slidingspeed, little wear on the rubbing surface, and little wear or scoring onan opposed rubbing surface.

Conventional friction materials, most of which are molded of a mixturemainly composed of asbestos fibers and including an organic binder, suchas phenol resin, together with fillers and additives, have not beenadequate to provide optimum properties as listed above.

Conventionally, friction materials molded of a mixture mainly composedof metallic material, such as cast iron, have also been used, but it iswell-known that these are not suitable for automotive brake liningmaterials because of their great expense (being serveral times asexpensive as those mainly composed of asbestos) and because of greatwear and scoring produced thereby on the opposed rubbing surfaces, andconsequently they have been mainly used for heavy railway equipment.

It is a primary object of the present invention to provide an improvedfriction material, and particularly an automotive brake lining material,having the above-listed optimum properties and which obviates thedefects in these respects of conventional friction materials.

A further important object of the invention is to provide an improvedfriction material which evidences less wear and scoring thanconventional friction materials under similar conditions of usage.

Another object of the invention is to provide a friction material whichmaintains a substantially constant coefficient of friction over a widerange of temperatures at its rubbing surface.

Still another object of the invention is to provide a friction materialwhich can be simply produced and which is economical to fabricate anduse.

The novel features that are considered characteristic of the inventionare set forth with particularity in the appended claims. The invention,itself, both as to its organization and its method of operation,together with additional objects and advantages thereof, will best beunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings, wherein likereference characters indicate like parts throughout the several figures,and in which:

FIG. 1 is diagram showing the relation between iron sand content andwear of friction materials with varying iron sand content;

FIG. 2 is a diagram showing the relation between iron sand content anddifference of maximum and minimum values of coefficient of friction ofeach sample, varied with temperature change;

FIG. 3 is a diagram showing the relation between the temperature at therubbing surface and the coeflicient of friction of friction materialsaccording to the present invention, and conventional materials; and

FIGS. 4(a) to -(d) are microphotographs showing wear and scoringappearing on the rubbing surface of a disc, when the disc is rubbed bythe friction material according to the present invention (FIGS. 4(a) and(b)) and by a conventional friction material (FIGS. 4(a) and The novelfeature which is considered characteristic of the present invention isthat iron oxide powder, whose main ingredient is ferrosoferric oxide,such as iron sand, is included as the main ingredient of the frictionmateral, instead of asbestos fibers which have been used conventionally.

The friction material, according to the present invention, contains ironoxide powder, mainly composed of ferrosoferric oxide, such as iron sand30-80% by weight, organic binder 15-65%, and the balance of (frictionmodifying) fillers and agents (additives) and is heated and molded by aconventional method. It has improved properties, such as less wear onits rubbing surface, constant coetficient of friction, and less wear andscoring on the opposite rubbing surface, and is particularly suitablefor automotive brake linings.

As a result of using iron sand, and the like, as the main ingredient,the total cost of material production is lowest because naturallyproduced iron sand can be obtained for a few percent of the most ofasbestos fibers.

Detailed ingredients of the mixture comprising the friction material ofthe present invention are described below.

For iron oxide powder mainly composed of ferrosoferric oxide, iron sand,which is naturally produced as magnetite powder, is used.

For organic binder, one or more kinds of conventional binders, such asphenol resin and modified phenol resins are used in the mixture.

For the fillers, one or more kinds of conventional fillers, such asbarite, graphite, litharge and kaolin are used in the mixture. Asbestosfibers are added in the present invention as one of the fillers, saidfibers being effective in the molding process to maintain uniformity ofmixture of the ingredients, and they contribute to improved quality ofthe product because of their fibrous characteristics.

For additives, one or more kinds of conventional additives, such as leaddioxide and manganese dioxide are used in the mixture.

The inventors have studied the plastic flow of ferrosoferric oxide (Fe Oapplied on a rubbing surface which occurs due to the frictional heatdeveloped thereon. Tests were carried out using friction materials withvarious contents of iron sand, which is well-known as iron oxide powderwhose main ingredient is ferrosoferric oxide.

The inventors have used three kinds of iron sand (A, B, C) which wereproduced as magnetic powder in three different places in Japan, andwhose ingredients are shown in Table 1. As will be apparent from thistable, their main ingredients are ferrosoferric oxide.

TABLE 1 Ingredients Feao T10 810; A110; percent Iron sand:

TABLE 2 Sample No 1 2 3 4 5 6 7 Ingredient:

Iron sand, percen 80 70 60 60 40 30 10 Resin, percent 20 30 40 50 60 7090 The Wear of Samples numbered 1 to 7 in the above table was measuredsubstantially in accordance with the testing method described byJapanese Industrial Standard D4411. That is, each sample was kept infrictional contact with a rotating disc made of steel (JapaneseIndustrial StandardS45C) for ten minutes under a normal load of 5.0kg./cm. at a sliding speed on the rubbing surface of 4.1 m./sec. whilethe temperature of the friction surface was kept at 100 C. constantly,by cooling.

The relationship between iron sand content and wear obtained by theabove tests are shown by the curve of FIG. 1, wherein the abscissa showsthe iron sand content and the ordinates show the amount of wear. It willbe observed that the wear gradually decreases up to about 40% of ironsand content and increases again above 50% of iron sand content. Inother words, wear becomes minimum at about 405 0% of iron sand content.

The samples numbered 1 to 7 were then tested to measure coefficients offriction with various rubbing surface temperatures according to the samemethod as described above except that the friction surface of eachsample was not cooled, but the temperature thereof was allowed to varybetween room temperature and 250 C. at its maximum. The results obtainedare shown in Table 3, below:

TABLE 3 Iron Difference of sand Degrees centigrade maximum content, andminipercent 50 100 150 200 250 mum values 80 0. 46 0. 49 0. 57 0. 60 0.52 0. 14 70 0. 44 0. 48 0. 56 0. 59 O. 52 0. 15 60 0. 42 0. 40 0. 56 0.59 0.47 0. 17 50 0. 43 0. 48 0. 54 O. 58 0. 41 0. 17 40 0. 43 0. 48 0.53 0. 57 O. 38 0. 19 30 0. 42 0. 46 0.53 0. 57 0. 29 0. 28 10 0. 42 0.470. 53 0. 55 0. 08 0. 47

In the right-hand end column of Table 3 is shown the difference ofmaximum and minimum values of coefficient of friction of each sampleover the range of temperature at the rubbing surface, as a means forshowing the degree of the variation of the coeflicient of friction withthe increase of temperature. The relation between the iron sand contentand the said difference between maximum and minimum values ofcoefiicient of friction is shown in FIG. 2, the former being plotted asabscissa against the latter as ordinates.

As is apparent from Table 3 and FIG. 2, the variation of the coeflicientof friction due to the temperature change becomes great at about 30% andbelow of iron sand content, and at more than 40% of iron sand contentsaid variation becomes further smaller and substantially constant.

By another test described later (using Samples B and B presently to bedescribed), most conventional molded friction materials whose mainingredients were asbestos fibers showed wear of more than 3.4-3.5 cm./10 kgm., as compared to less than 2 cm./ 10" kgm., for the material ofthe invention with 40-50% iron sand content. It is apparent from thetest results shown in FIGS. 1 and 2 and in comparison with the wearamount of conventional friction materials that the amount of iron oxidepowder, whose main ingredient is ferrosoferric oxide, such as iron sand,may be set at a practically effective range of 30-80% to exhibit theimproved wear resistance which is one of the benefits and acharacteristic feature of the present invention.

In conventional friction materials, a preparation of 10% of organicbinder has been sufficient to mold the product, but in the presentinvention, more than 15% is required to retain the improved Wearresistance above-described. The upper limit of organic binder contentwas determined to be 65%, because when the iron sand content was at aminimum (30%) at least 5% of fillers and additives were required inorder for the material to exhibit the improved characteristics.

A pair of practical Samples A and A which are usable for automotivebrake lining, were manufacturede containing proper amounts ofingredients according to the present invention, in which iron sands werecontained in the most desirable amount, as follows:

The above samples were manufactured by a conventional molding process,using a mixture of the three kinds of iron sand shown in Table 1 andpassed through a No. mesh sieve, mixed uniformly with the otheringredients listed above. The mixtures were molded at a temperature ofC. under a pressure of kg./cm. in a metal mold.

Conventional friction materials B and B were prepared, to be comparedwith Samples A and A Sample B is a commercially available frictionmaterial for automotive brake lining, Akebono FTJ, made by Akebono BrakeKogyo Kabushiki Kaisha, Hanyu, Saitama-ken, Japan, whose main ingredientis asbestos fibers and which contains other ingredients such as bindersand fillers wherein the proportions are not publicly known. Sample B wasspecially molded by the same process as used to make Samples A and A itsingredients and their amounts being as listed below:

Sample: Wear (em kgm.) A 1.8 A 1.9 B 3.5 B 3.4

(2) The variation of the coefficient of friction with increase intemperature at the rubbing surface was very small and the coeificientremained practically constant above 100 C. for Samples A and A ascompared with Samples B and B as shown in Table 4, below:

TABLE 4 Rubbing surfacce temperature, Difference of In FIG. 3, theabscissa shows the temperature at the rubbing surface and the ordinatesshow coefiicient of friction. The coefficient of friction of Samples Band B increased with temperature at the rubbing surface until theyreached about 200 C. and then decreased with further rise intemperature. In contrast, the coefiicients of friction of Samples A andA were substantially con stant over the range of temperature above 100C.

The stability of coefiicients of friction of Samples A and A with theincrease of temperature of the rubbing surface is also apparent from theright-hand end column of FIG. 4, which shows the difference valuebetween maximum and minimum coefiicients of friction of each sample inthe range of the rubbing surface temperature. Samples A and A accordingto the present invention, exhibited a small difference value of 0.15,while Samples B and B representing conventional materials, exhibited arelatively large difference value of 0.35.

(3) The wear and scoring on the disc (the opposed rubbing surface) wereextremely small for Samples A and A as compared with Samples B and B Thewear and scoring may be observed on the microphotographs, shown as FIGS.4(a)(d), enlarged about 25 X2.4 times. Only very indistinct streaks wereobserved on the disc when it was rubbed by Samples A and A as shown inFIGS. 4(a), and (b), while clear streaks were observed when the disc wasrubbed by Samples B and B as shown in FIGS. 4(a) and (d).

Thus, it is apparent that friction material according to the presentinvention has a characteristic feature in that it produces less wear andless scoring on an opposed rubbing surface than previously knownmaterials. The inventors believe that this eifect is due to the plasticflow of ferrosoferric oxide, which is the main ingredient of iron sand,such plastic flow not being expected from iron oxide 6 whose mainingredient is not ferrosoferric oxide, or from cast iron. It is believedthat this effect can be obtained only by friction materials such asthose of the present invention, including substantial amounts offerrosoferric oxide.

In the case of automotive brakes, a drum in a brake disc or a disc in adisc brake, employed as the opposed surface engaged by a brake lining,is not replaced by a new one periodically as is done in the case ofwheels for railway cars. It is, therefore, necessary to minimize wearand scoring of such opposing surfaces due to friction with the brakelining in the case of automotive brakes as much as possible so that thedrum, disc, or corresponding opposing surface can survive long periodsof use. At the same time, it is necessary to maintain a sufficientcoefficient of friction to provide adequate braking.

Friction material according to the present invention fulfills thesestrict requirements. As is apparent from the above-mentioned testresults, the novel characteristics of the invention are as follows: theWear is extremely small; the coeflicient of friction changes very littleand remains nearly constant with increase of temperature at the rubbingsurface; wear and scoring on the opposed rubbing surface are low; andmanufacture is economical. For these reasons, friction materialsaccording to the present invention are especially useful for automotivebrake lining materials.

Although certain specific embodiments of the invention have been shownand described, it is obvious that many modifications thereof arepossible. The invention, there fore, is not to be restricted exceptinsofar as is necessitated by the prior art and by the spirit of theappended claims.

What is claimed is:

1. A brake lining material having a substantially constant coefficientof friction and relatively low abrasive properties comprising by weight30-80% iron oxide powder whose main ingredient is ferrosoferric oxide,such as iron sand, organic binder 1565%, and the balance of fillers andadditives.

2. A friction material according to claim 1, wherein the proportion ofiron sand ranges between 40-50%.

3. A friction material according to claim 1, comprising 50% iron sand,24% phenol resin, 10% asbestos fibers, 8% barium sulfate, 6% polymer ofcashew nut shell oil, and 2% lead dioxide.

4. A friction material according to claim 1, comprising 40% iron sand,24% phenol resin, 20% asbestos fibers, 8% graphite, 6% polymer of cashewnut shell oil, and 2% manganese dioxide.

References fiited UNITED STATES PATENTS 3,092,595 6/1963 Smith et al260-38 X 3,434,998 3/1969 Aldrich et al. 26038 OTHER REFERENCES Rose etal.: The Condensed Chemical Dictionary, 5th ed., Reinhold Publ. Corp.,New York, 1956, p. 602.

MORRIS LIEBMAN, Primary Examiner S. M. PERSON, Assistant Examiner US.Cl. X.R.

106--36; 260DIG 39

